Adaptive MAC Protocol for a Cable Modem

Cable plants were initially designed for one-way broadcast communication (from the head-end to the neighborhood). They are now being upgraded to provide an upstream path (from the home to the head-end). New challenges arise in using the upstream channel since the available bandwidth is low and the noise levels are high. In this paper we present a MAC protocol especially designed to eeciently share the scarce upstream capacity. The protocol dynamically adjusts operating parameters to the current workload on the system. The control mechanism does not require any framing structure and is built around a \sea of mini-slots". The performance under both static and highly dynamic loads is close to optimum. The station implementation is particularly simple and the downstream control structure is also simple. Results are given here for xed length data units (ATM cells) but the algorithm extends very simply to variable length MAC frames. 1 Head-End Station Buffer Downstream Upstream Figure 1: Logical Topology of an HFC System.